1. Field of the Invention
The present invention relates generally to communications networking, and more specifically, to allocating upstream bandwidth within a communications network.
2. Related Art
Architects of communications networks continuously seek to achieve an optimal balance among various network characteristics. Such characteristics include bandwidth demand and quality of service parameters, such as latency, loss, or priority. For example, data-over-cable networks presently are expanding the variety of services traditionally provided to subscribers. In addition to television broadcasts, cable providers are offering telephony, messaging, and Internet services. As a result, additional bandwidth is needed to support the timely delivery of these services. Moreover, traditional cable broadcasts primarily require one-way communication from a cable service provider to a subscriber's home. As interactive or personal television services and other nontraditional cable services continue to be offered, communications media used to support one-way communications must now contend with an increased demand for bi-directional communications.
In a conventional cable television communications network, a communications device (such as a modem) requests bandwidth from a headend device prior to transmitting data to its destination. The headend device allocates bandwidth to the communications device based on availability and the competing demands from other communications devices. Typically, bandwidth is available to transmit signals downstream to the communications device. However in the upstream, bandwidth is more limited and must be arbitrated among the competing communications devices.
The downstream channel carries the information used by the communications devices to govern upstream transmissions. In a DOCSIS-compliant system, MAP messages are sent downstream to provide information about time slot assignments for the upstream channels associated with the downstream channel. In other words, the MAP messages assign one or more upstream channels to a specific communications device. The MAP messages also specify a time that may be used by the communications devices to transmit on an upstream channel and the type of data that may be transmitted. Moreover, these MAP messages are used by the headend device to predict the arrival of data from a communications device, the source of the data, and the type of data expected.
A headend device generally has one downstream channel and a finite number of upstream channels. To increment the quantity of upstream channels, the headend device can be chained to a second headend device through a master-slave interface. The first device runs in master mode, while the second device runs in slave mode. The master device sends MAP messages on its downstream channel across the master-slave interface to the slave device. The slave device, in turn, makes the MAP messages available to its upstream channels. If the master and slave devices each have, for example, eight upstream channels, using a master-slave interface permits the master device to receive data from a total of sixteen available upstream channels that can be used to support additional subscriber services.
Although a master-slave interface provides an avenue for supporting additional services, several drawbacks are attributable to this conventional approach. First, all upstream channels must be associated with a single downstream channel such that the upstream channels only receive MAP messages from the single downstream channel. Typically, master MAP messages are sent downstream from the master device to arbitrate asynchronous communications among the upstream channels of the slave device. If the slave device accepts the master MAP messages, no MAP message produced by the slave device can be used to arbitrate the upstream channels. In other words, if the downstream channel of the master device is associated with the upstream channels of the slave device, the downstream channel of the slave device cannot be used. Similarly, if less than the total available upstream channels of the slave device are associated with the downstream channel of the master device, the remaining upstream channels in the slave device cannot be used.
Conventional master-slave configurations are also inflexible and difficult to modify. The channel associations are fixed by the construction of the hardware. Therefore, the channel associations can only be changed by reconfiguring the hardware, namely to disable the master-slave interface. This cumbersome arrangement is not accommodating to changing load conditions in a dynamic, real time environment. The lack of system flexibility manifests an inefficient use of costly silicon and/or board resources.
Therefore, a communications device configured to support flexible channel association is needed to address the above problems.